Selenium is an essential trace mineral in the human body. This nutrient is a component of glutathione peroxidase, an important enzyme that protects arteries and cell membranes from damage by free radicals that are produced during normal oxygen metabolism. The body has developed defenses, such as antioxidants, to control levels of free radicals because they can damage cells and contribute to the development of chronic diseases. Selenium is also essential for normal functioning of the immune system and thyroid gland. Selenium may also aid in protein synthesis, growth and development, and fertility, especially in the male. It has been shown to improve sperm production and motility.Selenium has a variety of functions but its main role is as an antioxidant. It is part of a nutritional antioxidant system that protects cell membranes and intracellular structural membranes from lipid peroxidation. This protection of the tissues and cell membranes may benefit the cardiovascular system and protect against cancer. We need adequate daily amounts of selenium for the maintenance of these antioxidant functions and for selenium's other cellular functions as well. Selenium may also have anti-carcinogenic effects. The exact mechanism of action remains unknown. The most likely reason is related to its antioxidant action. However, some evidence suggests that selenium may decrease cell division or help cell repair.Selenium also seems to protect us from the toxic effects of heavy metals and other substances. People with adequate selenium intake have fewer adverse effects from cigarette smoking, alcohol, oxidized fats, and mercury and cadmium toxicity. Aside from the likely antioxidant influence, the specific mechanism by which selenium affords this protection is not known, though the effect is confirmed by some research. Plant foods are the major dietary sources of selenium. The amount of selenium in soil determines the amount of selenium in the plant foods that are grown in that soil. Low soil levels of selenium are associated with higher cancer rates, and soil-rich areas have below-average cancer rates for a number of body systems, particularly the breasts, colon, and lungs. Selenium also can be found in some meats and seafood. In the U.S., meats and bread are common sources of dietary selenium. Some nuts, in particular brazil nuts and walnuts, are also very good sources of selenium. |
